Since the discovery of a room temperature ferromagnetism in a graphite nodule from the Canyon Diablo meteorite[1] and the proton-irradiated graphite[2], there has been increasing interest in ferromagnetism in carbon-based materials including carbon nanotubes. In this work we have studied material property changes in single-walled carbon nanotubes (SWCNTs) under proton irradiation of various energies (1~18MeV) and doses (1.0•10-2 ~ 1.0•10-7 nC/µm2) using Raman spectroscopy. For a high energy proton irradiation (~18MeV) no significant change in Raman spectra after the proton irradiation was observed. But, for low energy proton irradiations (1~6MeV), some of the semiconducting SWCNTs exhibit an exceptional resistance to the proton irradiation damage. We have observed blue-shifts of the D-band and the G'-band Raman frequencies as well as a striking change in the relative Raman intensity of the D-band with respect to the G-band Raman intensity after the proton irradiation.
[1] J. M. D. Coey et. al., Nature 420, 156 (2002).
[2] P. Esquinazi et. al., Phys. Rev. Lett. 91, 227201 (2003).
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